1. Field of the Invention
The present invention relates to an ink jet recording medium and a recorded product.
2. Discussion of Background
In recent years, reflecting wide use of computers and digital cameras, hard copy technology to record images thereof on e.g. paper sheets has been developed. As hard copy recording systems, e.g. an ink jet system, a melting type thermal transfer system, a sublimation type thermal transfer system and an electrostatic transfer system have been known. Among these, an ink jet system has been widely used in recent years, since full-colored recorded products having a high image quality can be obtained, and the printing noise is low. Along with demands for high speed recording and high accuracy, it has been required for a recording medium to have high level of characteristics.
As the ink jet recording medium, a recording medium comprising a substrate and an ink-receiving layer made of a porous layer containing an alumina hydrate formed on the surface of the substrate, has been known (JP-A-2-276670). This recording medium is excellent in ink absorptivity, in the property for fixing colorants in the ink, and also in transparency of the porous layer, whereby an image having a high color density and a good color reproduction property can be obtained. Further, it has excellent characteristics as a recording medium, such as a high image quality and a high glossiness. Further, since it has a high transparency, it is also applied to sheets for an overhead projector.
It is an object of the present invention to provide a recording medium with which a recorded product having a high durability, particularly a high light resistance and ozone resistance, can be obtained, while maintaining the above-mentioned characteristics of the recording medium comprising a substrate and a porous layer containing an alumina hydrate formed on the substrate.
The present invention provides an ink jet recording medium which comprises a substrate and a porous layer containing an alumina hydrate formed on the substrate, wherein Mg ions and SCN ions are contained in said porous layer.
In the present invention, Mg ions and SCN ions are contained in the porous layer containing an alumina hydrate, whereby light resistance and ozone resistance will improve. This effect is considered to be mainly due to effects by the SCN ions, and it is considered that the Mg ions also have effects to increase the light resistance and the ozone resistance. In a case where Ca ions instead of the Mg ions are contained in the porous layer containing an alumina hydrate, although the Ca ions will not particularly inhibit the effect of the SCN ions, the colorants in the ink tend to aggregate due to the Ca ions, whereby the ink absorptivity of the porous layer may decrease, such being undesirable.
The Mg ions and the SCN ions are preferably contained in a form of a salt so that they easily dissociate as ions when the ink is imparted to the porous layer. A mixture of a salt containing the Mg ions and a salt containing the SCN ions may be contained, or a salt containing the Mg ions and the SCN ions may be contained. The Mg ions and the SCN ions may be contained as a salt containing other ions. However, if a large amount of other ions co-exist, the printing property may be influenced, and accordingly, the Mg ions and the SCN ions are preferably contained as a salt containing the Mg ions and the SCN ions alone, particularly as Mg(SCN)2.
In the present invention, the substrate is not particularly limited, and various ones may be used. Specifically, plastics including polyester resins such as polyethylene terephthalate and polyester diacetate, polycarbonate resins, fluororesins such as ETFE, and polyvinyl chloride resins, paper sheets and synthetic paper sheets may, for example, be preferably used. Further, cloths, glass and metals are also used. Such a substrate may be subjected to a corona discharge treatment or undercoating, in order to e.g. improve the bonding strength of the porous layer. Particularly when an opaque plastic film containing a white pigment or a paper sheet is used as the substrate, a recorded product equal to a silver halide photography can be obtainable.
In the present invention, the porous layer containing an alumina hydrate functions to absorb inks and to fix colorants. As the alumina hydrate, boehmite is preferred in view of transparency, color reproduction property, ink absorptivity and property for fixing colorants. Here, boehmite is an alumina hydrate represented by the compositional formula Al2O3.nH2O (n is from 1 to 1.5).
In the present invention, the porous layer containing the alumina hydrate preferably has an average pore radius of from 5 to 20 nm, and a volume of pores having pore radii of from 1 to 100 nm of from 0.3 to 2.0 cc/g. If the average pore radius or the volume of pores of the porous layer is beyond the above-specified range, no adequate ink absorptivity tends to be obtainable. Here, the pore characteristics are measured by a nitrogen adsorption/desorption method.
When the Mg ions and the SCN ions are contained in an equivalent amount, i.e. the SCN ions are contained in an amount of 2 moles per 1 mole of the Mg ions, the content is preferably such that Mg(SCN)2 is from 1.5 to 45 wt % based on the alumina hydrate. If the content of Mg(SCN)2 is less than 1.5 wt %, no adequate effect may be obtainable. On the other hand, if it exceeds 45 wt %, the ink absorptivity or resolution may decrease. The more preferred content of Mg(SCN)2 is from 4.5 to 25 wt %.
As a method to have the Mg ions and the SCN ions contained in the porous layer containing the alumina hydrate, specifically, a method of forming the porous layer containing the alumina hydrate, and then imparting an aqueous solution containing the Mg ions and the SCN ions thereto, followed by drying, is preferred. As the method of imparting the solution, preferred is an impregnation method or a spray method. Further, a material containing the Mg ions and the SCN ions may preliminarily be added to a material for forming the porous layer containing the alumina hydrate.
The porous layer containing the alumina hydrate preferably contains a binder together with the alumina hydrate. As the binder, an organic high polymer such as starch or its modified product, a polyvinyl alcohol or its modified product, SBR latex, NBR latex, carboxymethyl cellulose, hydroxymethyl cellulose or polyvinyl pyrrolidone may be used. The amount of the binder is preferably from 5 to 50 wt % based on the alumina hydrate. If the amount of the binder is less than 5 wt %, the strength of the porous layer containing the alumina hydrate may be inadequate, and if it exceeds 50 wt %, the property for absorbing and fixing inks may be inadequate.
As the method for forming the porous layer containing the alumina hydrate on the substrate, preferred is a method of adding the binder and a solvent to the alumina hydrate to obtain a coating fluid, and coating the fluid on the substrate followed by drying. As the solvent for the coating fluid, an aqueous one is preferred. It is preferred to use an alumina sol as the material for the alumina hydrate, since a porous layer having an excellent transparency and glossiness can be formed. As the method for coating the coating fluid, a dye coater, a roll coater, an air knife coater, a blade coater, a rod coater, a bar coater, a comma coater or the like may be employed.
The thickness of the porous layer containing the alumina hydrate is optionally selected depending upon the mode of printers or absorptivity of the substrate. When the substrate has no absorptivity, the thickness of the porous layer is preferably from 5 to 100 xcexcm. If the thickness of the porous layer is less than 5 xcexcm the ink absorptivity and the property for fixing colorants may be inadequate, and if it exceeds 100 xcexcm, the strength of the alumina hydrate layer may decrease. When the substrate has no absorptivity, more preferred thickness of the porous layer is from 10 to 50 xcexcm.
Further, when the substrate has absorptivity, the thickness of the porous layer is preferably from 1 to 50 xcexcm. If the thickness is less than 1 xcexcm, the ink absorptivity and the property for fixing colorants may be inadequate, and if it exceeds 50 xcexcm, the strength of the alumina hydrate layer may decrease. When the substrate has absorptivity, more preferred thickness of the porous layer is from 1 to 30 xcexcm.